The Alternating Current-Plasma Display (AC-PDP) uses a multi-subfield display technology to realize multiple grayscale levels for displaying an image. Different subfields have different weights (representing that the numbers of sustain pulses of different subfields are different). Multiple grayscales for displaying an image are realized via a combination of the subfields of different weights.
The multi-subfield display technology has a problem of false contour in a moving image. This is due to on one hand, the physiological characteristics of human eyes will move with the movement of an object; and on the other hand, the integral effect of vision. The perception of the human eyes to images and colors is the integral of the colors and brightness within a period of time. Hence, when multiple subfields are used to realize the multiple grayscale levels of an image, for a moving image, a phenomenon will appear that some places of the image are too bright or dark, which disappears once the moving image stops moving. The phenomenon that some places of the image are bright or dark alternatively is called a dynamic false contour phenomenon, which is a problem within the principle of the display technology and will be further discussed below.
Assume that one field of image is divided into eight subfields: SF1, SF2, SF3, SF4, SF5, SF6, SF7 and SF8, and the weights thereof are 1, 2, 4, 8, 16, 32, 64, and 128, respectively. Assume that an image moves from the left to the right, and there are two grayscale levels of 127 and 128 on the moving image. With the above mentioned weights of the subfields, the code for the grayscale level 127 is 11111110, and the code for the grayscale level 128 is 00000001. When the grayscale level is transiting from 127 to 128, the 8th subfield of the display grayscale 127 is not lighted, and the 1st, 2nd, 3rd, 4th, 5th, 6th and 7th subfields of the grayscale 128 are also in an unlighted state. Thus, since the order for displaying the subfields of the grayscale 127 is from the 1st subfield, the 2nd subfield, until the 8th subfield, the subfields following the 8th subfield are all in an unlighted state, and when entering the 1st, 2nd, 3rd, 4th, 5th, 6th and 7th subfields for displaying the grayscale 128, it is still in an unlighted state. Hence, from the 8th subfield of the grayscale 127 to the 7th subfield of the grayscale 128, the integrated grayscale of the human eyes to the image is 0, and thus a dark fringe appears, as shown in FIG. 3. In the same way, when the image is moving from the left to the right, a bright fringe also appears. Such dark fringe and bright fringe are the dynamic false contours.
See from the above principle, the dynamic false contour appears between image frames, different grayscale transitions between adjacent frames are integrated multiple times in the human eyes, if the result of the integral is the brightness perceived by the human eyes within one field of time. As known from FIG. 2, eight subfields are taken as an example, the integral of the human eyes has been made eight times during the transitions between different grayscales of adjacent fields, and each time a grayscale level is perceived, and if the grayscale levels of the eight perceptions greatly deviate from the display grayscale level, the human eyes perceive the dynamic false contour. For example, for the transition from grayscale 127 to grayscale 128, the codes in the order from the 1st subfield to the 8th subfield are 11111110 and 00000001, and the results of eight times of integrals according to the figure are 127, 63, 31, 15, 7, 3, 1, 0 and 128, respectively. During this process, when the result of the integral is 0, due to the severe deviation from the display grayscale level, the human eyes perceive the dynamic false contour. Hence, how to detect the dynamic false contour in an image and take corresponding optimized measures for the coding of the grayscale plays an obvious role for improving the quality of the image.